CO2 set to hit levels not seen in 50 million years by 2050

We are pumping carbon dioxide into the atmosphere so fast that it could soar to its highest level for at least 50 million years by the middle of this century.

And that’s even worse news than it sounds, because the sun is hotter now than it was then.

This is one of the conclusions of a study looking at how CO2 levels in the atmosphere have changed over the past half billion years and comparing that with future scenarios. “CO2 in the past was not as high as we thought,” says Gavin Foster at the University of Southampton in the UK.

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Thanks to bubbles of air trapped in Antarctic ice, we have a good picture of CO2 levels over the past 800,000 years. But going further back in time is much more challenging.

Foster and his colleagues have compiled data from more than 100 different studies to produce the best estimate yet of how CO2 levels changed in the past 420 million years. Among other things, the researchers corrected for the fact that studies based on carbonates in fossil soils are now known to have overestimated past CO2 levels.

Their compilation suggests that the concentration of CO2 in the atmosphere never rose above 3000 parts per million during this time period, whereas some earlier studies have suggested levels were as high as 5000 ppm at times. And by looking at future CO2 emission scenarios, they say the level will soon reach its highest for at least 50 million years – at around 600 ppm.

What’s not in doubt is that when CO2 levels were higher than in pre-industrial times, the planet was much warmer and had no ice at the poles.

Balancing factors

The gradual rise in the sun’s warmth over the past half a billion years has been balanced by a long-term decline in CO2 levels, says Foster, keeping the planet’s temperature in the habitable zone – with a little help from plants.

Land plants help break down volcanic rocks that react with CO2 and remove it from the atmosphere. This activity increases as the planet warms, and falls when it cools.

“Plant-driven weathering processes are too slow to save us from global warming, but they can be accelerated by applying crushed silicates to croplands to capture CO2,” says David Beerling at the University of Sheffield, who is leading a project to explore how much difference this could make.

But unless we manage to capture stupendous amounts of CO2 with methods like this, we’re headed into uncharted waters.